In this paper, a novel smart vibration energy harvester (VEH) is presented. The harvester automatically adjusts its natural frequency to stay in resonance with ambient vibration. The proposed harvester consists of two piezoelectric cantilever beams, a tiny piezomotor with a movable mass attached to one of the beams, a control unit, and electronics. Thanks to its self-locking feature, the piezomotor does not require energy to fix its movable part, resulting in an improvement in overall energy demand. The operation of the system is optimized in order to maximize the energy efficiency. At each predefined interval, the control unit wakes up, calculates the phase difference between two beams, and if necessary, actuates the piezomotor to move its mass in the appropriate direction. It is shown that the proposed tuning algorithm successfully increases the fractional bandwidth of the harvester from 4% to 10%. The system is able to deliver 83.4% of the total harvested power into usable electrical power, while the piezomotor uses only 2.4% of the harvested power. The presented efficient, autotunable, and self-sufficient harvester is built using off-the-shelf components and it can be easily modified for wide range of applications.
In this paper, a four hot-arm U-shape electrothermal actuator that can achieve bidirectional motion in two axes is introduced. By selectively applying voltage to different pairs of its four arms, the device can provide actuation in four directions starting from its rest position. It is shown that independent in-plane and out-of-plane motions can be obtained by tailoring the geometrical parameters of the system. The lumped model of the microactuator was developed using electro-thermal and thermo-mechanical analyses and validated using finite element simulations. The device has been fabricated using PolyMUMPs and experimental results are in good agreement with the theoretical predictions. Total in-plane deflections of 4.8 lm (2.4 lm in either direction) and upward out-of-plane deflections of 8.2 lm were achieved at 8 V of input voltage. The large achievable deflections and the higher degree-of-freedom of the proposed device compared to its counterparts, foresee its use in diverse MEMS applications.
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